ACOT9 is a mitochondrial acyl-CoA thioesterase that catalyzes hydrolysis of acyl-CoA thioesters into free fatty acids and coenzyme A, regulating cellular fatty acid and amino acid metabolism 1. Located on the inner mitochondrial membrane, ACOT9 preferentially deactivates short-chain fatty acyl-CoA while sparing long-chain substrates, directing acetyl-CoA toward the citric acid cycle rather than protein acetylation 2. This metabolic routing promotes hepatic glucose production and de novo lipogenesis, particularly under conditions of excessive nutrition 2. In hepatocellular carcinoma, ACOT9 expression is elevated due to miR-449c-3p downregulation and drives tumor growth and metastasis through lipid metabolism reprogramming, supporting poor prognosis 3. ACOT9 also suppresses thermogenesis by preventing acetyl-CoA utilization in brown adipocytes, promoting obesity development 4. Beyond cancer and metabolic disease, ACOT9 dysregulation associates with hyperlipidemia risk and rotator cuff disease susceptibility 56. In juvenile myelomonocytic leukemia, long non-coding RNA-mediated ACOT9 knockdown reduces cell viability 7. These findings identify ACOT9 as a potential therapeutic target for metabolic and malignant diseases.